富锂钼基层状正极材料的结构设计、储锂机制与表面改性

Lithium-rich manganese-based transition metal oxide solid solution zLi2MnO3-(1-z)LiMO2 (M = Ni, Co, Mn, etc.) is one of the most important high-capacity cathode materials for lithium ion batteries. However, issues such as low electric conductivity,the oxygen evolution reaction in the initial charge, and the high charge potential of its building block, Li2MnO3, result in problems such as poor rate performance and safety, and extra requirements to the electrochemical window of the electrolyte. This project is intended to alternate Li2MnO3 with Li2MoO3 or its doped cousins to construct novel lithium-rich layer-structured solidi-solution cathode materials zLi2Mo1-xMnxO3-(1-z)LiMO2. Features such as higher electric conductivity, lower delithiation potential and free of oxygen evolution are expected to be beneficial to enhancing the electrochemical performances of the new solid solutions. By controlling the composition and morphology of the precursors, we will optimize the structure and performances of the solid solution. With the help of various advanced in situ analytical techniques, the structure and the lithium storage mechanism of the new solid solutions will be explored. By computer simulation, the interaction mechanism of the Li-rich phase on cycling stability of the the solidi-solution will be clarified; by simulating the surface structural features of the solid soutions and their interaction with the electrolyte, principles for selecting the surface coating materials and the surface modification methods will be proposed.

富锂锰基层状过渡金属氧化物固溶体zLi2MnO3-(1-z)LiMO2 (M = Ni, Co, Mn等)是最重要的一类高比容量锂离子电池正极材料. 但是,由于构成单元Li2MnO3电导率较低、在首次充电过程中有析氧反应、充电电压过高等问题,导致该类材料倍率性能和安全性能差、对电解液要求高等缺点.本项目拟以安全性和循环性更好且充电电压平台较低的Li2MoO3及其掺杂化合物替代Li2MnO3,构建新的富锂层状固溶体正极材料zLi2Mo1-xMnxO3-(1-z)LiMO2.通过控制前躯体组分与形貌，优化固溶体材料的结构与性能。借助多种原位结构分析技术,探明其结构与储锂机制。通过计算机模拟,探明富锂相对固溶体材料循环稳定性的作用机制;通过模拟固溶体材料表面结构特点及与电解质的作用机制,提出表面改性材料的选择原则和表面改性方法.

合成纯相Li2MoO3并考察其在电化学脱锂过程中的结构变化以及在空气中长期储存的稳定性。通过第一性原理计算解释了虽然有过渡金属Mo提供电荷补偿但依然会发生MO离子向锂层迁移的驱动力，从多种元素中筛选出Sb部分替代Mo，稳定了脱锂过程中Li2MoO3的结构，提高了比容量。通过密度泛函结构设计，合成出钼基富锂氧化物材料Li1.2Mo0.6Fe0.2O2 (或记为Li2MoO3LiMo0.5Fe0.5O2)，通过促进过渡金属离子迁移，快速实现结构相变并将材料的放电电压和可逆容量稳定下来，保证了材料的结构稳定性和循环稳定性。.与此同时，我们也从实验和计算两个方面开展了富锂锰基正极材料的结构稳定研究。在通过第一性原理计算提出脱锂过程中Mn的迁移机制及其对材料结构和电化学性能影响的基础上，我们筛选出Nb作为掺杂元素，并通过实验验证了Nb掺杂对Li2MnO3的结构稳定作用。进一步地，我们通过全新的Nb表面改性方法，同时稳定了富锂锰基正极材料Li1.2Mn0.54Ni0.13Co0.13O2的比容量和放电电压。在经过100个循环后，材料比容量稳定在285 mAh g-1，放电电压衰减却只有190 mV(未经表面改性材料的电压衰减达到1000 mV)。这是一项非常具有应用前景的发现。此外，我们还在锂位对富锂锰基材料进行了Ti掺杂，也取得了较好的改性效果。